The present invention relates to scintillators, more particularly to methods and systems for discriminating between photon-related light emission and neutron-related light emission in contexts of detecting or observing scintillation.
Scintillators are materials that emit light when a gamma photon or a charged particle passes through its active volume and is absorbed. This light can be detected by an electronic light sensor such as a photomultiplier tube (PMT) or a photodiode. The light sensor generates light pulses when a photon or charged particle passes through the scintillator material that is optically coupled to it.
A scintillation detector (also known as a scintillation counter) is a type of radiation detector that includes a scintillator and an electronic light sensor to which the scintillator is optically coupled. The light sensor absorbs the light emitted by the scintillator, resulting in the generation of electrical (light) pulses that can provide information about the photons or charged particles that originally encountered the scintillator.
The height (magnitude) of a pulse is proportional to the total energy of the photon absorbed in the scintillator. These pulses can be sorted according to their heights through appropriate electronic processing, and stored in different channels of a device known as a multi-channel analyzer (MCA).
The plot of channel number versus the number of pulses in a channel is called a pulse height spectrum. The channels of the MCA are calibrated in terms of energy most commonly using the gamma photons with an energy of 662 keV emitted by the radionuclide 137Cs. This signal processing and storage enables the MCA to determine the gamma energy spectrum of a given radionuclide. The gamma energy spectrum is unique to a specific radionuclide and thus helps in its identification.
Neutrons are not capable of creating any light pulses by their direct interaction with the scintillator material, but are capable of producing charged particles when the neutrons are absorbed by specific nuclides such as 6Li, 10B, and a number of Gadolinium isotopes. Another process by which an incident fast neutron can produce a charged particle is by knocking out protons from hydrogenous materials.
Pulse shapes and pulse-height spectrums produced by charged particles differ in characteristics from pulse shapes and pulse-height spectrums produced via incident energetic photon interactions. However, the differences are not so extensive that the two categories of light emissions can be completely resolved from each other in the current state of the art. Therefore, there is a need to further improve the techniques to discriminate between the two distinct modes of energy release inside the active scintillator volume. The classical approach to differentiating between gamma and neutron signals is to study the pulse shape. The traditional assumption is that pulse-height spectrum is not sufficient to discriminate between gamma photons and neutrons.
Most gamma-sensitive scintillators lack the capability to detect neutrons. Conventional practice is to utilize two different types of scintillator materials to detect both gamma photons and neutrons. However, a new class of scintillators has been discovered that exhibit the phenomenon of core-valence luminescence (CVL). These scintillators emit core-valence luminescence (CVL), in addition to giving off self-trapped exciton (STE) and activator emissions.